Study data lacking on benefits and risks of medical marijuana for chronic pain and PTSD

August 24, 2017

By Tristan Horrom
VA Research Communications

"We don't have enough information to confidently answer [whether doctors should recommend cannabis] one way or the other."

Interest in medical marijuana has increased in recent years. But does it actually help with pain and other conditions? According to a literature review commissioned by the VA Quality Enhancement Research Initiative (QUERI), evidence is lacking on the effects of medical marijuana for many types of chronic pain and for PTSD.

Researchers from the VA Portland Health Care System and Oregon Health and Science University searched multiple databases for studies on marijuana use for treating chronic pain or PTSD, and for studies on the potential harms of marijuana use. They included studies on a wide variety of cannabis plant preparations, including marijuana cigarettes and plant extracts. Studies on synthetic cannabis were excluded.

The results of this review were published as two articles in Annals of Internal Medicine in August 2017, one on chronic pain and one on PTSD.

After reviewing more than 13,000 publications, the researchers identified 75 relating to pain or potential harms. They found limited evidence that marijuana use might alleviate neuropathic pain in some patients, and that it might reduce spasticity associated with multiple sclerosis.

There was insufficient evidence on the benefits of marijuana for all other pain types.

The body of evidence was limited by the number and size of studies, the inconsistency of results across studies, methodologic flaws of many available studies, and the lack of information on the long-term effects in chronic pain populations.

Very few studies on cannabis for PTSD

The researchers found insufficient evidence to assess the effects of marijuana on PTSD. Very few studies and no randomized controlled trials have been conducted on this topic. Three observational studies found that the marijuana use was not associated with PTSD symptom improvement.

In the largest of these studies, active marijuana use was associated with greater PTSD symptom severity. However, it is impossible to know from existing studies whether marijuana directly causes improvements or worsening in PTSD symptoms, say the researchers.

They also noted that there are multiple randomized controlled trials investigating the effectiveness of marijuana for treating PTSD currently underway. Evidence from these trials will likely be available in the next few years.

Lack of evidence 'surprising'

According to Dr. Devan Kansagara, senior author on the project, the lack of evidence was surprising: "We thought we would find more substantial evidence of beneficial effects, given how medical marijuana is widely used."

Additionally, his team found limited but consistent evidence that active marijuana use in general populations was associated with an increased risk of psychotic symptoms and psychotic spectrum disorders, adverse cognitive effects, and motor vehicle accidents. There was insufficient evidence to determine the long-term effects of marijuana use on cardiovascular health, on pulmonary health in older patients, and on the risk of many types of cancer.

The review also found almost no information about the long-term health effects of marijuana in older, sicker patients. The researchers cautioned that it is difficult to apply existing evidence to real-world clinical practice because dosage is often inaccurate and inconsistent in products available to patients through dispensaries. Moreover, many trials tested products that included equal and low levels of THC (the chemical associated with euphoria and possibly pain control) and CBD (a chemical that does not produce euphoria, but is thought to possibly help with pain control). In most dispensary products, the dosage of THC is far higher.

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Medical marijuana use increasing despite lack of evidence

As of this study, 29 states—plus Washington, D.C., Guam, and Puerto Rico—had legalized marijuana for medical purposes. Between 45 and 80 percent of those who seek medical marijuana do so for pain management, and up to 39 percent of patients on long-term opioid therapy for pain also use marijuana. More than a third of patients seeking medical marijuana list PTSD as the primary reason for their request.

As the researchers explain, marijuana is becoming commonly available through state-sanctioned dispensaries, despite limited research on benefits and harms. The popular press has reported many stories about people gaining relief by using marijuana as a coping strategy for pain and PTSD.

According to the researchers, more information is needed on the clinical effects marijuana, including studies comparing marijuana with other pharmacologic treatments and comparing different cannabis preparations. They explain that, while strong evidence of the benefits of medical marijuana has not been found, "clinicians will still need to engage in evidence-based discussions with patients managing chronic pain who are using or requesting the use of cannabis." At this point, any methodologically strong research would add to the strength of the available evidence, they say.

VA and federal position on marijuana

Current federal law prohibits the use or dispensing of marijuana. As a federal agency, VA follows this prohibition, even where individual state laws permit marijuana use. As such, VA does not prescribe medical marijuana to any of its patients.

Patients participating in state medical marijuana programs are not denied VA services, but VA doctors cannot complete forms giving recommendations or opinions about a patient's need for prescription marijuana. VA providers may need to consider patients' marijuana use in the context of substance use disorder programs, or to avoid health complications or possible drug interactions.

Although marijuana is illegal under federal law, the Controlled Substances Act allows for research into the potential medical uses of controlled substances. Such research must be approved by the Drug Enforcement Agency, Food and Drug Administration, National Institute of Drug Abuse, and scientific merit review boards.

VA is not currently conducting any research on the topic, but VA leadership has expressed interest in learning from ongoing research outside the agency. Kansagara agrees that more research will help shed more light on the actual benefits and risks. "We don't have enough information to confidently answer [whether doctors should recommend cannabis] one way or the other," he says. "We certainly need better research."

In a May 31, 2017, White House press briefing, VA Secretary Dr. David J. Shulkin summed up VA's position on medical marijuana: "Federal law does not prevent us at VA to look at [medical marijuana] as an option for Veterans. I believe that everything that could help Veterans should be debated by Congress and by medical experts, and we will implement that law. ...And we're interested in looking at [existing medical marijuana research] and learning from that. But until the time that federal law changes, we are not able to prescribe medical marijuana."